The invention relates to an attachment device for connecting plastic parts, particularly linings, to sheets, especially body components of a motor vehicle. It consists of a plastic body with a foot part for insertion into a hoop-shaped holder of the plastic part, and a head part, which, when assembled, projects through an opening in the sheet.
The British Patent No. GB 2,262,564 proposes a one-piece plastic injection-molded attachment device in which there are arrayed locking pieces that project at the periphery for locking in a circular hole. Following one-time assembly, though, the part can be loosened when damaged, owing to its configuration, and therefore cannot be used repeatedly.
The U.S. Pat. No. 5,058,356 describes an attachment device which serves to attach decorative components. In this part, a lockable metal spring in the component to be attached is p laced on a T-girder-shaped shaft. However, the part is quite expensive to manufacture.
Such attachment devices should connect a hole in the structural part and an essentially aligned hole in the sheet to each other in locking fashion, so that the connection can be made during assembly by applying pressure on the structural part. Additionally, disassembly must be possible by pulling off the structural part without destroying the attachment device or the sheet. The aim is to ensure that the attachment device is not visible on the outer side of the structural part. To accomplish this, often holders which are injection-molded in the form of a flat hoop, bear the hole to admit the attachment device.
The objective of the present invention is to provide an attachment device which meets the above-mentioned requirements and ensures a secure attachment with a long service life.
This objective is achieved according to the invention by placing on the head piece a metal clamp adjoining the head piece, both of whose arms form a stop spring which forms an acute angle to the longitudinal axis of the plastic body. When assembled, the stop springs push back the edges of the opening in the sheet. The head piece has projections which push back parts bent inward of the metal clamp's arms on the side of the head piece that faces the foot piece.
In addition to making possible a reliable attachment, the attachment device according to the invention allows simple assembly of the attachment device in the structural part, as well as of the structural part with the attached attachment device on the sheet. In particular, the attachment device according to the invention ensures that, through fixing of the position of the attachment device vis-a-vis that surface of the structural piece which comes into direct contact with the sheet during assembly, the sheet piece will become securely engaged. At the same time, the attachment device according to the invention provides support of the attachment device within the structural part, so that pressure is applied without deformation of the structural part on the attachment device during assembly.
One advantageous embodiment shape of the invention consists in having the head piece sit atop a narrower middle piece while forming the projections.
This embodiment shape is preferably further configured by having the head piece shaped essentially as a half cylinder, with its shell surrounding the plastic body and forming a contact surface for the metal clamp. This causes the holding force to be transferred from the sheet via the stop springs to the head piece.
To better balance the tolerances, provision is preferably made to have the bends of the arms and the head piece configured so that the metal clamp is swivel-supported on the head piece. However, this applies only in a not yet assembled condition. When assembled, the arms of the metal clamp are pressed together, so that the upper part of the metal clamp securely borders the head piece. In particular, the bends of the metal clamp then press on the edges, producing long-lasting tension if the plastic body is to be somewhat deformed by flow of material. In the case of a vehicle's interior lining, the result is no noise over a lengthy period.
A further advantageous embodiment consists in having the head piece configured at least partially as a roller shape. It is surrounded by the metal clamp at an angle which is greater than 180.degree., preferably 270.degree.. By this means, holding forces are advantageously applied to the head piece.
Yet another embodiment of the invention makes provision for the ends of the stop springs to be bent inward at an angle which ensures sufficient holding forces, but nonetheless permits disassembly by pulling the attachment device out of the sheet.
Using another configuration of the invention, the hole in the sheet is sealed by having the plastic body, at an interval from the foot piece, carry a plate-shaped sealing disc, whose edge lies on the sheet in an assembled state.
The attachment device according to the invention can also be configured so that the middle piece of the plastic body has a double-T shaped cross section, with one cross piece and two end pieces, with the end pieces overlapping the head piece. Thus, a lateral guide for the metal clamp is formed. Preferably, provision is made that lugs project in the area of the stop spring's ends, which limit the swivel angle of the metal clamp.